Generally, an agricultural chemical is a drug that can prevent the infection of the contagious pathogens including bacteria and fungi, prevent the occurrence of the disease even when infected or treat the disease. The agricultural chemical can act by inhibiting the growth or proliferation of the pathogen in some cases. The agricultural chemicals can be divided by the target site and mechanism. Firstly, the drugs containing various metal ions and dithiocarbamates such as Captan act by inhibiting the respiration of cytoplasm or mitochondria, and oxycarboxines act by inhibiting electron transfer system. Secondly, the drugs that inhibit the biosynthesis of the fungi are another kind of agricultural chemicals. For instance, blasticidine-S inhibiting protein biosynthesis, dicarboximides inhibiting biosynthesis of cell wall component chitin of fungi, pyrimidines, triazoles and imidazoles inhibiting steroid biosynthesis of cell membrane, tricyclazoles inhibiting cell membrane triglyceride biosynthesis and acylalanines inhibiting nucleic acid synthesis belong to this category. Thirdly, benomyls inhibit the proliferation by preventing the nuclear division. Fourthly, dodines inhibit the function of the cell membrane by the physical means. And fifthly, fosetyl-Al increases the resistance of the host plant.
One of the differences of Magnaporthe grisea that causes rice blast, one of the main rice diseases, is the fact that melanin pigment accumulates between he appressorium cell membrane and cell wall when Magnaporthe grisee invades and damages the plant If the pigment cannot accumulate inside the appressorium by preventing the biosynthesis of melanin pigment, this mechanism of action can be used in developing fungicides to prevent rice blast.
The thiazdine derivatives in preventing rice blast have been known. The structures of the representative compounds are shown as Formulas II-1, II-2, II-3, II-4, and II-5 [Swiss patent application number 755,894 (May 7, 1975), German patent 2,619,724(Nov. 18, 1976), U.S. Pat. No. 4,079,144 (Mar. 14, 1978), Japanese Patent Announcement No. 85,054,314 (Nov. 29, 1985), EP 683,160 (1995) (Chem. Abstr. 124:202283j), Fiziol. Akt. Veshchestva (USSR) 1976, 8, 109-112 (Chem. Abstr 87:48807s(1977), Geman Laid-Open Patent Publication No. 3,836,160 (1988) (Chem. Abstr. 113:128074w(1990), Geman Laid-Open Patent Publication No. 3836184 (1988) (Chain. Abstr 113:1 52457u (1990)), Ger (East) DD 241,844 (1985) (Chem. Abstr. 107:91901 m(1 987)). 
The problem of these agricultural chemicals including those shown above, however, is that fungus becomes resistant against these chemicals. Therefore, the chemicals become less effective even at higher concentrations. Therefore, to solve these problems, it is necessary to develop chemicals with tally different mechanism of action.